Most invasive species pose no direct threat to and have no immediate impact on human life; however, since its introduction in the 1940s, Eurasian watermilfoil (Myriophyllum spicatum) has wreaked havoc on inland bodies of water throughout the United States. The species has already invaded forty-four of the fifty states and its rapid proliferation causes swimming, boating, and fishing problems.
A proposed study at Duke University is seeking funding in order to investigate novel approaches to control of Eurasian watermilfoil. Because previous studies have already shown that Eurasian watermilfoil is susceptible to biological control via the milfoil weevil (Euhrychiopsis lecontei), the aim of the proposed study is to use this weakness to find other methods to control the invading watermilfoil.
The study, suggested by Duke undergraduate Emily Chang, focuses on the relationship between the Eurasian watermilfoil and the E. lecontei weevils. The weevils have been used to control the invading plant in other areas because they chew through the plant’s tissues, which results in the collapse, and death, of the plant. The proposed study looks to analyze the composition of the plants in terms of chemical elements, organic functional groups, and damaged nonstructural hydrocarbons after the weevils have invaded a population of Eurasian watermilfoil. Chang hopes that this information will provide insight into “the chemical nature of this biocontrol method” and will “allow scientists to improve the effects of biocontrol by manipulating the chemistry operating behind the watermilfoil.”
Chang states that “if milfoil can spread as much as it has, it is clearly very powerful and has the potential to spread everywhere.” Thus, in hopes to combat the spread of this invasive species, Chang has proposed a study that hopes to advocate the use of biocontrol as a stepping block for the expansion of chemical control. Currently, Chang feels that biocontrol is the only feasible method of dealing with Eurasian watermilfoil and notes that “mechanical control is bad because it is time consuming because each plant must be hand plucked and because milfoil is a resilient species. Chemical control is also a poor option because it only offers temporary relief.” However, Chang hopes to change this by using information from biological control to foster the development of chemical controls that will cause permanent effects.
Chang’s experiment will utilize four lakes that have substantial Eurasian watermilfoil populations. Four 3×5 meter plots will be created for analysis; one plot will be a control containing just the watermilfoil, and the other three plots will contain the watermilfoil with varying numbers of weevil population densities. The different plots will be monitored from May to October for three consecutives years. Once a month, fifteen plants will be removed from each plot, frozen, then dried and crushed and analyzed for carbohydrate concentration. Some methods of elemental analysis include the use of a CHN Analyzer, infrared spectroscopy (IR), and nuclear magnetic resonance spectroscopy (NMR). The plant samples will be compared to the original composition of watermilfoil before the study. On a side note, the contents of the weevils’ stomachs will also be analyzed in order to determine which tissues are targeted in feeding.
If specific carbohydrates are targeted by the milfoil weevils, the future of control could be very optimistic. Scientists would be able to focus on attacking the specific weak carbohydrates and functional groups in order to take down the invading Eurasian watermilfoil populations. Chang hopes to use chemical control to help thwart the dangers of watermilfoil and concludes that “if we can pinpoint which carbohydrates are favored, … we can apply certain chemical herbicides to cause plants to die and disappear.”